Page 78 - Chemistry ICSE Class X

66 ICSE Chemistry – 10
ƒ The bases which on dissociation/ionisation in aqueous solutions
ů;K,Ϳ ͕ &Ğ;K,Ϳ ĂƌĞ triacid bases͘ – –
3
3
produce three hydroxyl ions (OH ) or contain three OH ions (if
insoluble) per molecule of the base are called triacid bases.
3+
–
Al(OH) (aq) o Al (aq) + 3OH (aq)
3
ASSIGNMENT 3

Bases, Characteristics of bases, Classification of bases

ϭ͘ DĞŶƟŽŶ ƚǁŽ ĐŚĂƌĂĐƚĞƌŝƐƟĐƐ ŽĨ ďĂƐĞƐ͘
Ϯ͘ EĂŵĞ ƚǁŽ ĞĂĐŚ ŽĨ ;ĂͿ ^ŽůƵďůĞ ďĂƐĞƐ ;ďͿ /ŶƐŽůƵďůĞ ďĂƐĞƐ͘
ϯ͘ ;ĂͿ tŚĂƚ ŝƐ ŵĞĂŶƚ ďLJ ƚŚĞ ƚĞƌŵ ĂůŬĂůŝ͍
;ďͿ 'ŝǀĞ ƚǁŽ ĞdžĂŵƉůĞƐ ŽĨ ƐƚƌŽŶŐ ĂůŬĂůŝƐ͘
;ĐͿ 'ŝǀĞ ƚǁŽ ĞdžĂŵƉůĞƐ ŽĨ ďĂƐŝĐ ŽdžŝĚĞƐ ǁŚŝĐŚ ĂƌĞ ŝŶƐŽůƵďůĞ ŝŶ ǁĂƚĞƌ͘
ϰ͘ 'ŝǀĞ ƚŚĞ ŶĂŵĞ ĂŶĚ ĨŽƌŵƵůĂ ŽĨ
;ĂͿ Ă ĚŝĂĐŝĚ ďĂƐĞ
;ďͿ ŽŶĞ ŶŽƌŵĂů ƐĂůƚ ĂŶĚ ŽŶĞ ďĂƐŝĐ ƐĂůƚ ŽĨ ƚŚŝƐ ĚŝĂĐŝĚ ďĂƐĞ͘
ϱ͘ tƌŝƚĞ ƚŚĞ ďĂůĂŶĐĞĚ ĐŚĞŵŝĐĂů ĞƋƵĂƟŽŶƐ ĨŽƌ ƚŚĞ ŝŽŶŝƐĂƟŽŶ ŽĨ ;ĂͿ tĞĂŬ ŵŽŶŽĂĐŝĚ ďĂƐĞ ;ďͿ tĞĂŬ ĚŝĂĐŝĚ ďĂƐĞ
ϲ͘ ,Žǁ ǁŝůů LJŽƵ ĐŽŶĮƌŵ ƚŚĂƚ Ă ƐŽůƵƟŽŶ ŐŝǀĞŶ ƚŽ LJŽƵ ŝƐ Ă ďĂƐĞ͍
General Methods of Preparation of Bases

Bases can be prepared by the following general methods:

ƒ By synthesis
ƒ By the action of water on the soluble oxides of metals
ƒ By the action of water or steam on metals
ƒ By double-decomposition (or by precipitation method)
ƒ By thermal decomposition of some oxo salts.

Preparation of bases by synthesis (or by direct
combination)
Metallic oxides are basic in nature. Metals react with oxygen at room
temperature or on heating to form their oxides. Such oxides are bases.
room
4Na(s) + O (g) o 2Na O
2
2
sodium temperature sodium oxide
ignite
2Mg(s) + O (g) o MgO(s)
2
magnesium magnesium oxide
Preparation of bases by the action of water on the soluble
oxides of metals

Oxides of alkali metals and alkaline earth metals dissolve in water to give
alkali.

Na O(s) + H O(l) o 2NaOH(aq)
2
2
sodium oxide sodium hydroxide
CaO(s) + H O(l) o Ca(OH) (aq)
2
2
lime limewater
(calcium oxide) (calcium hydroxide)